The principal objectives of this research program are to analyze interactions occurring between embryonic CNS tissue that is implanted into the brains of adult mammals (rats) and the mature neurons of the host animal, which promote regeneration of adult axons into the embryonic implants and the growth of embryonic axons into the mature host CNS. Specifically, implants of embryonic CNS tissue will be allowed to interact with the septal and/or hippocampal regions of the adult rat brain by placing them in cavities produced by removing the entorhinal cortex and/or transecting the fornix/fimbria. Particular emphasis is to be placed on experiments which study: 1) the specificity of ingrowth of embryonic axons within the denervated host CNS, 2) the competition between various implant efferents and intrinsic axons within the denervated host target, and 3) the effect of the embryonic implant on regeneration of mature axotomized neurons in the CNS of the adult recipient.